The project is concerned with understanding the organization and interactions of lipids and proteins in a bacterial cytoplasmic membrane. The proposal describes the use of appropriate bacterial strains with mutations in membrane lipid biosynthesis for a series of chemical, physical, morphological, and biochemical experiments to delineate how fatty acid composition determines the distribution and properties of phospholipids and the permeability and enzymatic activities of the membrane. Furthermore, the biochemical mechanisms by which the cell conserves those properties of lipids important to structure and function will be investigated. Having identified in a relatively simple and well-defined system important properties of membrane lipids and control mechanisms for conserving them, we will initiate physical and biochemical experiments with various types of membranes from animal cells to explore the generality of these findings.